1. Field of the Invention
The invention relates to a sublance for use in performing measurements and/or taking samples in a metallurgical furnace. The principal use of such a lance is in a metallurgical furnace in which there is a main lance for supplying oxygen, where the sublance which has a probe at its lower end is dipped into a hot metal bath and withdrawn again.
Particularly, the invention will be described here to its application to a steel converter of the type in which liquid pig iron is converted to steel by means of top-blown oxygen from a main lance. However analogous applications of the invention are possible in metallurgical processes in other types of metallurgical furnaces.
2. Description of the Prior Art
In order that it is possible to monitor the progress of the refining process in the steel furnace and control it when necessary during the oxygen blowing, a sublance as described above is often used. During oxygen blowing, or during a pause in the oxygen blowing, the sublance is moved down towards the metal bath parallel to the main lance so that the probe can reach into the bath. The probe may be equipped with means for measuring the bath temperature and/or analyzing the concentration of certain elements such as carbon and oxygen in the bath. These measured values can then be transmitted from the probe to the exterior of the furnace via a cable extending through the sublance. It is also possible to use a probe in the form of a sample vessel, so that the sublance can take a sample from the pool, for analysis outside the furnace. The technique for the use of sublances to carry out such measurements and/or take samples is described in the literature.
A difficulty encountered in the use of such a sublance is that, if the sublance is lowered during oxygen blowing it is heated asymetrically by the furnace. This causes the sublance to bend, so that it may be useful for only a few measurements, or even only one measurement. A conventional method of overcoming this difficulty is to remove the lance from its suspension after use and to bend it straight elsewhere. It can then be remounted and used again.
The availability of the lance is thus limited, and operating and maintaining it require considerable labour. In particular, if the lance is of the liquid-cooled type, the connections for the liquid cooling need to be removed and replaced each time it is bent straight.
Another difficulty in the conventional use of the sublance is that, as a result of its bending, the data obtained with it have limited reproducibility.
U.S. Pat. No. 4,141,249 describes a construction in which the sublance is mounted so as to be rotatable about its axis so that, after the sublance has been used once, resulting in its being bent, it can be rotated through 180.degree. so that the bend is reversed. During subsequent use of the lance, it will be bent back again by the heating more or less to the original straight condition.
Typically the sublance has, within its outer body, several concentric passages, e.g. for downward and return flows of cooling fluid and for a cable connected to the probe. In the lance of U.S. Pat. No. 4,141,249, this leads to a rather complex and difficult arrangement at the connections to the rotatable lance. Because of the operational environment of the lance, these connections must not be delicate or liable to failure.